Writing on ZDNet in response to some mad ravings by Huffington Post blogger Russell Shaw, George Ou offers the best explanation of QoS ever:
I’ll say this loud and clear; QoS is a reordering of packets that is an essential part of network traffic engineering. Take the following example where A represents VoIP packets and b represents webpage packets.
No enhanced QoS policy
AbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbAbAbbbbbbAbAWith enhanced QoS policy
AbbbbbbbbbAbbbbbbbbbbAbbbbbbbbbbAbbbbbbbbbbANow note that there are only 5 A packets in the entire stream for either scenario and you still get the exact same throughput for the b packets with or without prioritization for the VoIP A packets. The difference is that the A packets are now a lot more uniform which makes sound quality go up and the webpage b packets don’t really care about uniformity since all they care is that they get there at all intact. With this QoS example, you can improve VoIP without affecting the average throughput of web surfing. More precisely, QoS has ZERO throughput effect on non-prioritized when there is zero congestion on the pipe. If it had been a congested network, then QoS will have minimal effect on non-prioritized traffic.
All those who think “net neutrality” regulations are fine should read this article and try to understand it. He breaks the issues down with great clarity and anybody who thinks he can regulate the Internet had better be able to understand what he’s saying.